Bi-directional switches switch high currents through their conduction electrodes while blocking high voltages applied to the conduction electrodes. Bi-directional switches are used in a variety of electrical systems. A typical bi-directional switch is specified to supply high currents, which can range from several Amperes of maximum current to several hundreds of Amperes depending on the specific switch and application, while blocking relatively high voltages, e.g. of at least 25 V without breaking down.
Bi-directional switches are typically implemented using electromechanical switches or a configuration of semiconductor devices, e.g. power transistors. However, standard power transistors have no technically meaningful blocking voltage in one direction, making them unidirectional devices. Consequently, current bi-directional switches typically are implemented using two separate serially coupled power MOSFETs. The separate MOSFETs are formed on separate semiconductor dice, and often housed in separate packages, which results in a high manufacturing cost and a large area occupied on a circuit board. When the separate MOSFET dice are housed in a single package and interconnected with wire bonds, the area occupied on a circuit board is reduced but the manufacturing cost is still too high for many applications.
U.S. Pat. Nos. 7,282,406, 7,297,603, 7,537,970, 7,910,409, 8,101,969 and 8,530,284 all disclose an integrated circuit with several different transistors integrated on the same circuit, including a p-channel bi-directional trench power transistor for battery charging protection. The transistor comprises two vertical trenches between which a body is present. The body is separated from current carrying electrodes above and below the body by high-voltage regions with a lesser doping concentration than the electrodes. However, this bi-directional trench power transistor has an inherent parasitic bipolar transistor formed by the body and the high voltage regions. Furthermore, it is not suitable for operation with high voltages, such as of at least 20 or more, e.g. up to 40 V or more, and/or high currents, e.g. above 1 mA, up to 1 A or more.
U.S. Pat. No. 8,101,969 discloses a body bias switch including two MOSFETs connected in parallel to the native diodes in the bi-directional trench power transistor. The MOSFETs are integrated on the same die as the bi-directional trench power transistor. When the drain voltage is the highest voltage (i.e. out of the drain voltage and the source voltage), the body is referenced to the source voltage, and vice versa when the source voltage is the highest voltage, the body is referenced to the drain voltage. However, this bias switch comes with a risk of over-voltages damaging the MOSFETs since the gates of the MOSFETs are connected directly to the drain and source respectively. Accordingly, in case the maximum drain-source voltages of the bidirectional transistor exceed the breakdown voltages of the MOSFETs the latter risk irreversible damage.